Bug 1534: Changed blocking calls to async in dist data store

Changed the read and commit methods to use async akka actor calls instead of
submitting tasks to a ListeningExecutorService that do blocking akka
calls. This obviates the need for the ListeningExecutorService.

Change-Id: I7a3f369917431067ad1817a3ab53a358bc21f123
Signed-off-by: tpantelis <tpanteli@brocade.com>
Merge "Bug 1534: Changed blocking calls to async in dist data store"